Lecture 6: Bacterial Motility + Introduction to pili/fimbriae Flashcards
What are the different types of flagella?
- Monotrichous
- Amphitrichous
- Lophotrichous
- Peritrichous
Describe Monotrichous flagella
Just one flagella at the end of the cell
Describe Amphitrichous flagella
Flagella at either end of the cell
Describe Lophotrichous flagella
multiple flagella at either end of the cell
Give an example of a bacteria that has Monotrichous flagella
Vibrio cholerae
Give an example of a bacteria that has Amphitrichous flagella
Campylobacter jejuni
Give an example of a bacteria that has Lophotrichous flagella
(Helicobacter pylori)
Describe Peritrichous
flagella
Grow flagella all over the cell i.e e coli
Give an example of a bacteria that has Peritrichous flagella
e coli
What do motility patterns alternate between?
Run and tumble
Describe bacterial movement (run and tumble)
- Run: motor rotates anti clockwise. The flagellar filaments form bundle and propel cells
- Tumble: quick reversal of motor to clockwise rotation. This produces a twisting force that transforms the flagella into a righthanded helix. The bundke falls apart rapidly
- Run: motor rotates anti-clockwise again. The flagellar filaments form a bundle and propel in a new direction.
What are the 4 tactic responses of bacteria
Aerotaxis
Chemotaxis
Magnetotaxis
Phototaxis
Describe aerotaxis
movement usually towards oxygen
Describe Chemotaxis
movement usually towards nutrients but also away from toxins
Dewscribe Magnetotaxis
movement along lines of magnetism
Describe Phototaxis
movement towards light
Explain how chemotaxis in bacteria works
- Transmembrane proteins called Methyl-accepting chemotaxis proteins (MCP) stick out of cells and detect and measure changes in environment
- These interact with cytoplasmic proteins called che proteins which interact with rings of motor regulating direction in which it turns (dictate of the cell runs or tumbles)
What is another name for MCP transmembrane proteins?
transducer proteins
How many different MCPs does e coli have?
5, which each detect different compounds
What happens when MCP interacts with sensor kinase CheA?
The sensor kinase CheA autophosphorolates
What happens when a bacteria is in the presence of an attractant?
The concentration of phosphorylated sensor kinase CheA decreases, anti-clockwise motion, longer runs
What happens when a bacteria is in the presence of a repellent?
The concentration of phosphorylated sensor kinase CheA increases, clockwise motion, more tumbling
What does CheA-P phosphorolate?
CheY
What does CheY-P bind to ?
The flagellar motor
What happens when CheY-P binds to the flagellar motor?
There’s a change from anti-clockwise rotation to clockwise rotation, and the bacteria tumbles
What dephosphorylates CheY-P?
A phosphatase, CheZ. This allows the anti-clockwise motion to resume
How does a bacterial cell integrate the signals of attractants and repellants ?
By using CheR to methylate the MCP. The more methyl groups the MCP has, the less sensitive it is to the attractant and the repellent.
CheB increases methylesterase activity and the demethylation of the MCP
Low conc. attractant
high CheA-℗, high CheB-℗
Demethylation of MCP, increasing sensitivity to attractant (longer runs)
High conc. attractant
low CheA-℗, low CheB-℗
High methylation level of MCP, decreasing sensitivity to attractant, increasing autophosphorylation of CheA (more likely to tumble)
is it true that each MCP receptor binds different ligands and different species have different optimum niches ?
Yes
What is it called when a bacteria moves without the flagella?
Gliding
Which bacteria is gliding common in ?
cyanobacteria
How quickly does F. johnsoniae glide?
at up to 10 µm/s
Describe how F. johnsoniae glides
Latex spheres added to F. johnsoniae bind to and are rapidly propelled along cells
Suggests that adhesive molecules move laterally along the cell surface during gliding
What are the genes associated with gliding?
gld genes
What happens if you disrupt gld genes?
- You get a loss of motility
- increases resistance to bacteriophages that infect wild-type cells
- loss of the ability to digest the insoluble polysaccharide chitin
Describe twitching motility via type IV pilus
- Based on type IV pili first extending from cell surface then being retracted, dragging cell along surface
- Powered by ATP hydrolysis
- Retraction proteins control direction of movement
Which bacteria can gas vesicles be found in?
In planktonic bacteria (e.g. cyanobacteria), and some archaea
What are gas vesicles?
Protein vesicles that contain gas, which confers buoyancy to the cell
Describe how gas vesicles work
Allow cells to float up to oxygenated water or towards the light
Can be involved in vertical migration in aquatic systems such as lakes
What are fimbriae/pili?
Surface appendages, multi-subunit proteins
What do fimbriae/pili do?
Allows for adhesion to other bacteria, host cells or environmental surfaces
What are specialied pili associated with?
genetic exchange between bacteria
How do some researchers distinguish between fimbriae and pili?
by linking pili to conjugation and gene exchange, but this is not always true
What tests have defined at least 7 groups of pili?
Traditional agglutination tests
What do agglutination tests use?
use yeasts, red blood cells, or tissue culture cells with or without mannose inhibition
What are the most important pili?
type I and type IV
Are fimbiae and pili major determinants of bacterial virulence?
Yes, they allow pathogens to attach to (colonise) tissues
Is it true that fimbiae and pili sometimes aid resistance to immune cell phagocytosis?
Yes
Because fimbriae are antigenic, what are there antigens called?
Colonisation Factor Antigens (CFA)
What antibodies detect the fimbriae/pilli and block bacterial colonisation?
Secretory antibodies (IgA)
What antibodies detect the fimbriae/pilli and catalyse phagocytosis?
Circulating antibodies (IgG or IgM)
Role of fimbirae/pili in adhesion
- Loose association of microbe with mucus
- Pili and fimbriae allow microbe cell to stick to the surface of the epithelial cell. Tip protein binds to glycolopid receptors on epithelial cell.
- Pili pulls microbe cloe to the host cell
- Microbe becomes invasive (into or through submucosal epithelial cells
)
-
